Windshield wipers are manually controlled by the driver of a vehicle when rain or moisture has accumulated on a window. A driver must repeatedly actuate a wiper control in a light drizzle condition when continuous-on wiping is inappropriate. Thus there is a need for automatic wiper systems which actuate the wipers only when moisture is detected and which does not require manual actuation.
Assemblies for automatically energizing a wiping system on a vehicle have included a control circuit to sense a variable amount of moisture on the surface of a window. Such circuits have included capacitive sensors situated on the exterior of the window of a vehicle which are responsive to water droplets. When moisture collects on the window, the capacitance is changed. The change in capacitance is detected which in turn energizes a wiper means.
One type of such assembly includes a pair of parallel sensor wires extending from the exterior of window to a detecting circuit within a vehicle. The detecting circuit includes an oscillator with a frequency proportional to the value of the capacitance created by the pair of sensor wires. As moisture collects on the window, the value of the capacitance changes which changes the frequency of oscillation. The change is frequency is detected by a frequency to voltage convertor which sends a d.c. signal to a comparator to compare the d.c. signal to a reference voltage and actuate a wiper means if lower. The U.S. Pat. No. 4,554,493 granted Nov. 19, 1985 in the name of Howard L. Armstrong discloses such a capacitive sensing assembly. The problem with this assembly is that leads extend from the sensor to the control circuit.